Typically, transition ducts have an aft frame which is attached, or integrated into, the aft end of the duct, facilitating attachment of the duct to the inlet of the turbine first stage. The aft frame is often cooled by means of controlled seal leakage and small cooling holes that allow compressor discharge air to pass through the frame. It has proven difficult, however, to cool the aft end of transition ducts which do not have an aft frame integrally formed with, or attached to the duct body. In accordance with exemplary but nonlimiting implementation of this invention, forced convection and potentially impingement cooling are used as a means to directly cool a transition duct which does not have an aft frame structure.
Accordingly, in one aspect, the present invention relates to a transition duct for a gas turbine comprising: a tubular body having a forward end and an aft end; a plurality of cooling channels formed on an exterior surface of the tubular body at the aft end; a closure band surrounding the aft end, covering at least a portion of the plurality of cooling channels; and a seal attached to the closure band, surrounding the aft end of the tubular body.
In another aspect, the present invention relates to a method of providing cooling air to an aft end of a gas turbine transition duct comprising: forming plural open cooling channels on an exterior surface of the transition duct at the aft end thereof, the plural cooling channels extending from an aft edge of the duct in an upstream direction; closing at least a portion of the plural open cooling channels with a peripheral closure band to thereby form cooling passageways; and incorporating a seal into the closure band.
The invention will now be described in greater detail in connection with the drawings identified below.